Lemma 1 [1]} Suppose the characteristic polynomial \(F(\xi )\)  of a second order Jacobian matrix is given by \(F(\xi ) = \xi ^2 - a_1 \xi + a_2\) . Then the solutions \(\xi _i,~ i = 1, 2,\)  of \(F(\xi ) = 0\)  satisfy \(\mid \xi _i\mid < 1\)  for \(i = 1, 2,\)  if the following conditions hold:
\((i)~a_2 < 1,~ (ii)~ 1 + a_2 > \mid a_1 \mid .\) 
